The invention relates to communications systems generally and, more particularly, the invention relates to information distribution systems delivering one or more a relatively low bandwidth information streams as information sub-streams of a relatively high bandwidth information stream.
In several communications systems the data to be transmitted is compressed so that the available bandwidth is used more efficiently. For example, the Moving Pictures Experts Group (MPEG) has promulgated several standards relating to digital data delivery systems. The first, known as MPEG-1 refers to ISO/IEC standards 11172 and is incorporated herein by reference. The second, known as MPEG-2, refers to ISO/IEC standards 13818 and is incorporated herein by reference. A compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, and is incorporated herein by reference.
MPEG and MPEG-like information streams may be spliced together in a relatively seamless manner by defining xe2x80x9cIn Pointsxe2x80x9d and xe2x80x9cOut Pointsxe2x80x9d for each stream that are indicative of, respectively, appropriate stream entry and exit points. An MPEG-like information stream that contains such In Points and Out Points is said to be spliceable. The Society of Motion Picture and Television Engineers (SMPTE) has proposed a standard SMPTE 312M defining such splicing points entitled xe2x80x9cSplice Points for MPEG-2 Transport Streams,xe2x80x9d which is incorporated herein be reference in its entirety.
Many information providers, such as television studios, continue to make substantial investments in equipment conforming to a serial digital interface defined in SMPTE standard 259M. The SMPTE 259 interface was originally developed to carry PAL and NTSC-format digital video in a particular uncompressed form and with a sampling rate of exactly 27.000 MHz. To help preserve this investment, a standard is emerging within SMPTE to carry other forms of video and audio over SMPTE 259. This emerging standard is often referred to as the Serial Data Transport Interface (SDTI) standard or SMPTE 305M. The SMPTE 259 standard and proposed SMPTE 305M standard are incorporated herein by reference in their entireties.
The proposed SMPTE 305M standard specifies a data stream used to transport packetized data, such as MPEG-like data, within a television studio or production center environment in a manner compatible with SMPTE 259. Thus, relatively low bitrate MPEG streams (e.g., 30 Mbps) may be transported within a studio environment as a sub-stream of a relatively high bitrate SDTI stream (e.g., 270 Mbps or 360 Mbps).
Unfortunately, the SMPTE 305M standard does not provide a solution to the problem of sub-stream splicing. Specifically, to seamlessly splice an MPEG stream carried in an SDTI stream, the MPEG stream must be removed from the SDTI stream, spliced with another MPEG stream (possibly within a respective SDTI stream) and inserted back into an SDTI stream. This is because typical switching equipment switches or edits SMPTE 259 streams only at frame boundaries.
Therefore, it is seen to be desirable to provide a method and apparatus that allows seamless splicing of MPEG information streams carried within SDTI streams. More generally, it is seen to be desirable to provide a method and apparatus that allows seamless splicing of any frame delineated or segmented information stream carried as a sub-stream within a relatively higher bitrate, frame delineated or segmented information stream.
The invention provides a low cost method and concomitant apparatus for incorporating one or more relatively low bitrate information streams (e.g., MPEG) into a relatively high bitrate information stream (e.g., SDTI) in a manner aligning low bitrate sub-stream splice entrance points and splice exit points within the frame boundaries of the high bitrate information stream. In this manner, the splicing of the relatively high bitrate information stream at appropriate In Frames and Out Frames will provide relatively seamless splicing of information sub-streams. Additionally, the packing and unpacking methods are implemented such that the temporal offset between elementary streams carried within relatively low bitrate information stream is removed, i.e., the elementary streams are synchronized.